The present invention relates to a paper feed control device which is installed in a copier for controlling a paper feed level to a predetermined one by moving up and down a tray which is loaded with a stack of papers by means of a motor or the like.
In a high-speed copier, it sometimes happens that before a document is fed by an RDF (recirculation document feeder) or an ADF (automatic document feeder) to a predetermined copying station, several papers have been fed from a paper feeding device. Paper end, therefore, needs to be detected before the tray is emptied, i.e., while several papers are still left in the tray.
It has been customary to estimate a remaining amount of papers based on a level, or height, of the tray. Specifically, when the tray has been raised beyond a certain reference level, it is determined that a paper-end or near-paper-end condition is reached in order to avoid an occurrence that papers are used up during the course of copying cycles. Usually, a level of the tray is determined by counting up pulses which an encoder mounted in the paper feeding device generates during upward and downward movements of the tray. Meanwhile, various kinds of papers are used with a copier and they differ in thickness, for example. It follows that for the same number encoder output pulses a comparatively large number of papers may have been left if the paper thickness is small and a comparatively small number of papers is otherwise. In this manner, the prior art system for sensing a remaining amount of papers lacks in reliability.